The present invention relates to a support for a natural human heart which may be used for the surgical correction of a deformed heart valve, specifically a heart valve which has become dilated. In particular, the present invention relates to a holder and flexible annuloplasty ring prosthesis combination for properly positioning the ring about the valve annulus during implantation.
The human heart generally includes four valves. Of these valves the more critical ones are known as the mitral valve, which is located in the left atrioventricular opening, and the tricuspid valve, which is located in the right atrioventricular opening. Both of these valves are intended to prevent regurgitation of blood from the ventricle into the atrium when the ventricle contracts. In preventing blood regurgitation both valves must be able to withstand considerable back pressure as the ventricle contracts. The valve cusps are anchored to the muscular wall of the heart by delicate but strong fibrous cords in order to support the cusps during ventricular contraction. Furthermore, the geometry of the heart valves ensure that the cusps overlay each other to assist in control ling the regurgitation of the blood during ventricular contraction.
Diseases and certain natural defects to heart valves can impair the functioning of the cusps in preventing regurgitation. For example, certain diseases cause the dilation of the heart valve annulus. Dilation may also cause deformation of the valve geometry or shape displacing one or more of the valve cusps from the center of the valve. Other diseases or natural heart valve defects result in deformation of the valve annulus with little or no dilation.
Dilation and/or deformation result in the displacement of the cusps away from the center of the valve. This results in an ineffective closure of the valve during ventricular contraction, which results in the regurgitation or leakage of blood during ventricle contraction. For example, diseases such as rheumatic fever or bacterial inflammations of the heart tissue can cause distortion or dilation of the valvular annulus. Other diseases or malformations result in the distortion of the cusps, which will also lead to ineffective closure of the valve.
One method of repairing an impaired valve is to completely replace the valve. This method is particularly suitable for replacing a heart valve when one of the cusps has been severely damaged or deformed. While the replacement of the entire valve eliminates the immediate problem associated with a dilated valve annulus, presently available heart valves do not possess the same durability as natural heart valves. Various surgical procedures have been developed to correct the deformation of the valve annulus and retain the intact natural heart valve.
These surgical techniques involve repairing the shape of the dilated or elongated valve. Such techniques, generally Known as annuloplasty, require surgically restricting the valve annulus to minimize dilation. Typically, a prosthesis is sutured about the base of the valve leaflets to reshape the valve annulus and restrict the movement of the valve annulus during the opening and closing of the valve.
A suitable prosthesis should allow the surgeon to properly reconstruct the heart valve annulus and minimize dilation, while allowing natural movement of the valve annulus during the opening and closing of the valve. The ability of the prosthesis to allow for a natural opening and closing of the valve is particularly important since such prostheses are not normally removed from the heart valve, even if the valve annulus heals to a normal geometry.
Many different types of prostheses have been developed for use in annuloplasty surgery. In general prostheses are annular or partially annular shaped members which fit about the base of the valve annulus. Initially the prostheses were designed as rigid frame members, to correct the dilation and reshape the valve annulus to the natural state. These annular prostheses were formed from a metallic or other rigid material, which flexes little, if at all, during the normal opening and closing of the valve.
Examples of rigid annuloplasty ring prostheses are disclosed in U.S. Pat. Nos. 3,656,185, issued to Carpentier on Apr. 18, 1972; and 4,164,046, issued to Cooley on Aug. 14, 1979. Certain artificial heart valves have also been developed with rigid frame members similar to the rigidity of the described valve prosthesis. Examples of this type of heart valve are disclosed in U.S. Pat. Nos. 4,204,283, issued to Bellhouse et al on May 27, 1980; and 4,306,319, issued to Kaster on Dec. 22, 1981.
Rigid annuloplasty ring prostheses adequately promote the healing of the valve annulus by restricting valve dilation and reshaping the valve annulus. However, this rigidity prevents the normal flexibility of the valve annulus. That is, a normal heart valve annulus continuously flexes during the cardiac cycle, and a rigid ring prosthesis interferes with this movement. Since the prosthesis remains implanted, even after the valve annulus has healed, a prosthesis of high rigidity will permanently restrict the normal opening and closing of the valve, and thus impair the normal functioning of the valve. Another disadvantage with a highly rigid ring prosthesis is the tendency of the sutures tearing during the normal movement of the valve annulus.
Other workers have suggested the use of completely flexible annuloplasty ring prostheses. Flexible prostheses include an inner support member formed from a flexible material. This support member is wrapped in woven, biocompatible cloth material. Resistance to the dilation of the annulus during the opening and closing of the valve is obtained by the proper suturing of the ring about the valve annulus.
One disadvantage with completely flexible ring prostheses is that during the implantation process the material forming the ring may become bunched at localized areas. This bunching of the prosthesis results in the phenomenon known as multiple plications of the ring prosthesis. One result of this phenomenon is variability of the ability of the ring to control the shape of the valve annulus. The bunched up areas of the ring tend to provide a more rigid area in comparison to the other portions of the ring which results in distorting the valve annulus during the opening and closing of the valve.
Examples of completely flexible ring prostheses are disclosed in U.S. Pat. No. 4,290,151, issued to Massana on Sep. 22, 1981, and are discussed In the articles of Carlos D. Duran and Jose Luis M. Ubago, "Clinical and Hemodymanic Performance of a Totally Flexible Prosthetic Ring for Atrioventricular Valve Reconstruction", 5 Annals of Thoracic Surgery, (No. 5), 458-463, (Nov. 1976) and M. Puig Massana et al, "Conservative Surgery of the Mitral Valve Annuloplasty on a New Adjustable Ring", Cardiovascular Surgery 1980, 30-37, (1981).
Still further types of annuloplasty ring prostheses are designed to allow for adjustment of the ring circumference, either during the surgical implantation, or as the ring prosthesis during the opening and closing of the valve. This type of adjustable prosthesis is typically designed in combination with a rigid, or at least partially rigid frame member.
An example of a self adjusting ring prosthesis is taught in U.S. Pat. No. 4,489,446, issued to Reed on Dec. 25, 1984. This annuloplasty ring prosthesis provides for self adjustment of the prosthesis annulus by two reciprocating pieces which form the prosthesis frame. The basic disadvantage of this ring prosthesis is that the individual frame members are formed from a rigid material, with the resulting prosthesis suffering the same disadvantages discussed above for rigid ring prosthesis in general.
Other examples of adjustable ring prostheses are taught in U.S. Pat. Nos. 4,602,911, issued to Ahmadi et al and 4,042,979, issued to Angell on Aug. 23, 1977, provide for mechanism of adjusting the ring circumference. In Ahmadi et al the ring prosthesis frame is a coiled spring ribbon which is adjusted by a mechanical screw assembly. In Angell, a drawstring is used to adjust the circumference of a rigid frame member. Again, these ring prostheses suffer from the disadvantages of the rigid ring prosthesis discussed above. The Angell prosthesis could also possess a substantially flexible portion after suturing which could include multiple plications for the reasons discussed above for the completely flexible prosthesis.
U.S. Pat. No. 4,055,861, issued to Carpentier on Nov. 1, 1977 teaches an annuloplasty ring prosthesis which has a flexibility between the completely flexible rings discussed above and rigid ring. The ring of Carpentier is deformable to an equal degree and simultaneously in all directions. The preferred support is described as having the elasticity of an annular bundle of 2 to 8 turns of a cylindrical bristle of poly(ethylene terephthalate).
While rigid and semi-rigid annuloplasty rings provide a benefit over flexible rings, the restrictive nature of such rings may be detrimental to the ability of the valve to normally open and close. It thus remains an object to provide a flexible annuloplasty ring which does not have the any of the above described detriments.